Antiskid brake controllers have been in widespread use for many years. In the simplest sense, an antiskid brake controller compares the speed of a vehicle (e.g., automobile, aircraft, etc.) derived from a wheel speed sensor to the vehicle speed derived from a secondary or reference source. If the wheel is determined to be skidding an excessive amount, then brake pressure applied to the wheel is released and the wheel is allowed to spin back up to the appropriate speed.
A fundamental problem associated with virtually all antiskid brake controllers relates to determining an appropriate amount of skidding. Two types of controllers which are generally known utilize different techniques. The first type of antiskid controller is deceleration based. In short, the deceleration based controller differentiates the wheel speed to determine how fast the wheel speed is changing. If the wheel decelerates too quickly, there is said to be excessive skidding and the controller reduces the amount of pressure transmitted to the brakes.
A second type of antiskid controller relies on a model of the mu-slip curve which describes the tire-to-road surface friction characteristics. The difference between the wheel velocity and the vehicle velocity is referred to as the slip velocity. The slip velocity is compared with a predefined set point on the mu-slip curve in order to achieve a desired amount of skidding.
Antiskid controllers which are based on the mu-slip curve are oftentimes computationally complex and require multiple sensors for measuring wheel speed, vehicle speed, etc. Consequently, deceleration based antiskid controllers may be preferred as a simpler approach. However, deceleration based antiskid controllers in the past have not been sufficiently adaptive to adjust to varying tire/surface conditions (e.g., wet or icy conditions) insofar as determining an acceptable amount of skidding. Failure to adjust for varying conditions can result in the antiskid controller prematurely releasing brake pressure and/or failing to adequately control excessive skidding.
In view of the aforementioned problems associated with conventional antiskid brake controllers, there is a strong need in the art for a controller which is adaptive to handle changing tire/surface conditions. In addition, there is a strong need for such a controller which is not computationally intensive and which does not require multiple sensors, etc.